The present invention generally relates to optical disk recording/reproducing apparatus for recording and/or reproducing information signal on and from an optical disk by means of an optical beam, and in particular to an optical recording/reproducing module used in such an optical disk recording/reproducing apparatus for producing and focusing the optical beam on the optical disk, in which an optical system for producing, guiding and focusing the optical beam on the optical disk and an electrical system for modulating and/or demodulating the information signal on and from the optical beam are accommodated in a common housing.
An optical disk recording/reproducing apparatus records and/or reproduces an information signal on and from a rotary optical disk by means of an optical beam. For this purpose, the optical disk recording/reproducing apparatus uses an optical recording/reproducing system comprising an optical system for producing, guiding and focusing the optical beam on the optical disk, and an electrical system for modulating and/or demodulating information signal on and from the optical beam.
Conventionally, such an optical recording/reproducing system has a linearly aligned configuration of a laser diode for producing the optical beam, a collimator lens for shaping the optical beam to form a parallel optical beam and an objective lens for focusing the parallel optical beam on a recording surface of the optical disk. Such an optical recording/reproducing system is disposed perpendicularly to the plane of the optical disk. Further, the conventional optical recording/reproducing system comprises a beam splitter provided in the aforementioned linearly configured optical path so as to divert an optical beam reflected back from the optical disk perpendicularly to the first mentioned linear optical path to a photo detector included in the optical system after passing through an array of a plano-convex lens and a cylindrical lens. Typically, the electrical system comprises a drive circuit for driving the laser diode and a processing circuit for processing the electrical signal produced by the photo detector, and the electrical system is disposed further below the optical system. Such an optical recording/reproducing system has a problem of large size and is contradictory to the requirement of size reduction of the optical disk recording/reproducing apparatus.
Further, there is a known optical recording/reproducing module having an optical path extending parallel to the optical disk. This optical path connects various optical elements such as a laser diode, photo detector, collimator lens, plano-convex lens, cylindrical lens, beam splitter and the like and extends parallel to the optical disk. Further, the optical path is deflected by a mirror in a direction perpendicular to the plane of the optical disk and the optical beam thus deflected is focused on the optical disk through an objective lens. In such a recording/reproducing module, the optical system is accommodated in a generally rectangular-shaped flat box or housing. The housing has an opening on its top side for allowing entrance of various optical elements at the time of assembly and this opening is closed by a cover lid. Further, a focusing actuator carrying the objective lens projects upwards from the top side of the housing. The housing is usually disposed below the optical disk such that the flat housing extends parallel to the disk. On the other hand, the electrical system for driving the laser diode and for processing the output electrical signal of the photo diode is provided on a circuit board which is provided remote from the housing accommodating the optical system.
In such a conventional optical recording/reproducing module, there is a problem that a space surrounding the focusing actuator which is extending upwards from the top side of the housing and also a space formed above the optical system in the housing are not used at all. In order to achieve size reduction of the optical disk recording/reproducing apparatus, such an unused space should be eliminated. Further, in such an optical recording/reproducing module, there is another problem that a relatively long wire has to be used for connecting the laser diode or photo detector in the optical system to a cooperating circuitry in the electrical system, since the electrical system is provided at a location which is relatively distant from the location where the optical system is provided. The use of such a long connection wire is undesirable as the chance that the faint electrical signal produced by the photo detector picks up electromagnetic interference when the signal is transmitted through the wiring is increased. In order to avoid such an interference, the conventional optical recording/reproducing module uses a specially designed wire such as a coaxial cable and a corresponding connector. However, such a coaxial cable and corresponding connector are heavy and the use of them invites increase in weight of the recording/reproducing apparatus. Further, as a consequence of the use of connectors, the conventional optical recording/reproducing module tends to suffer from electrostatic breakdown of semiconductor devices which occasionally occurs when the cable is connected.
Further, when using the aforementioned construction having an optical path extending parallel to the optical disk for recording the information signal on the optical disk, there arises another problem of cooling the electrical system, as a high output power laser beam has to be produced at the time of recording. The aforementioned construction is particularly disadvantageous as the opening at the top of the housing is closed by a cover lid for preventing the invasion of dust into the housing, and the heat released from the semiconductor chips tends to be accumulated in the housing. Such an accumulation of heat in the housing invites an undesirable temperature rise in the optical system in the housing.